FORAMINIFERA 



6i 



marks, or on the so-called littoral shelf exteiuliiiLi,' to deep water ; 

 they are for the most part adherent to seaweeds, or lie anion*^ 

 sand or on the niiul. Other forms, again, are pelagic, snch as 

 Glohigerina (Figs. 1.3, 6, 16, 17) and its allies, and float as part 

 of the plankton, having the surface of their shells extended by 

 delicate spines, their pseudopodia long and radiating, and the outer 



Fig. 12. — Lieberkvhnia, a fresli-water Rliizopod, fruin the egg-shaped shell of wliicl 

 branched pseudopodial tilameiits protrude. (From Yervvorn.) 



part of their cytoplasm richly vacuolated ("alveolate"), and pro- 

 bably containing a lic^uid lighter than sea water, as in theKadiolaria. 

 Even these, after their death and the decay of the protoplasm, 

 must sink to the bottom (losing the fine spines by solution as they 

 fall) ; and they accumulate there, to form a light oozy mud, the 

 " Globerina-ooze " of geographers, at depths where the carbonic 

 acid under pressure is not adequate to dissolve the more solid 

 calcareous matter. Grey Chalk is such an ooze, consolidated by 



